1. Field of the Invention
The present invention relates to a compound acoustic actuator drive circuit suitable for use in a portable information terminal having variations in the vibration resonant frequency of a compound acoustic actuator.
2. Related Art
A compound acoustic actuator is used to generate vibration and sound, making use of the principle of a dynamic speaker, and are used in portable information terminals such as cellular phones to generate a sound or vibration when a call is received. A compound acoustic actuator has vibration resonant frequencies corresponding to a sound and to a vibration. In general, when a signal having a frequency equal to the lower resonant frequency is input, the compound acoustic actuator operates as a vibrating body, and when a signal having a frequency equal to the higher frequency is input, the compound acoustic actuator operates as a sound generator, in either case the vibration or sound notifying the user of the portable information terminal of the receipt of a call.
FIG. 10 of the accompanying drawings shows the general construction of a compound acoustic actuator, in which when an electrical signal at an audible frequency is input to a coil 34, a driving force is generated between the coil 34 and the magnetic circuit 33, so that a sound is generated by the vibration of a diaphragm 35. If the frequency of the electrical signal input to the coil 34 coincides with the resonant frequency of the mechanical vibrating system formed by the magnetic circuit 33 and a suspension spring 32, the magnetic circuit 33 vibrates, and the vibration is transmitted to a case 31 via the suspension spring 32.
FIG. 11 shows the measured values of the vibration characteristics of two compound acoustic actuators, A and B, at a nominal frequency of 132 Hz. From these measurement results, it can be seen that there is a dispersion of approximately 1 Hz in the vibration resonant frequency R0Real with respect to the nominal value. The Q being a high value, there is a great decrease in the vibration amplitude at frequencies which are not the vibration resonant frequency f0Real thereof (in this case fOA and fOB).
For example, it is possible to obtain a maximum vibration amplitude (acceleration) as indicated in the vibration characteristics of the compound acoustic actuator A in the case in which the resonant frequency f0=132 Hz is input to the compound acoustic actuator A. However, the vibration amplitude obtained for the case in which the resonant frequency f0=132 Hz is input to the compound acoustic actuator B drops to approximately 76% of the maximum value of the compound acoustic actuator B. In a compound acoustic actuator, therefore, in order to achieve a sufficient amount of vibration, it is necessary to apply a signal coinciding in frequency with the vibration resonant frequency of the compound acoustic actuator.
As shown in FIG. 12, therefore, in a configuration in which an electrical signal of a pre-established frequency is generated by a signal generator 1 and amplified by an amplifier 2, the amplified signal being input to the compound acoustic actuator 3 so as to generate either a sound or a vibration, there is the problem of a large dispersion in the amount of vibration. To compensate for this problem, a transducer is proposed as disclosed in the Japanese Patent No.2963917, in which an individual vibration resonant frequency R0Real is detected, and the frequency of the drive signal is automatically adjusted to this detected frequency R0Real.
This conventional technology, however, is accompanied by the following problems. Specifically, there is an increase in cost that is incurred because of the complexity of an automatic tracking circuit that must be provided so as to search for the vibration resonant frequency f0Real for each individual device.
Accordingly, it is an object of the present invention to provide a driving waveform that suppresses a reduction in the amount of vibration caused by dispersion in the vibration resonant frequency of a compound acoustic actuator, and further to provide a drive circuit of simple configuration for generating this driving waveform.
In order to achieve the above-noted objects, the present invention adopts the following technical constitution.
Specifically, a first aspect of the present invention is a signal generation circuit for a compound acoustic actuator that generates a sound and a vibration in response to a frequency of a signal input to the compound acoustic actuator, the signal generation circuit comprising: a plurality of signal data stored in a memory to generate a plurality of signals having mutually different frequencies, the plurality of signals at least including a signal, a frequency of which is equal to a resonant frequency causing the compound acoustic actuator to generate the vibration, a synthesizing means to synthesize a plurality of drive signals in accordance with the plurality of signal data so as to cause the compound acoustic actuator to generate the vibration, and a sweeping means to sweep the plurality of drive signals, repeatedly.
In the second aspect of the present invention, the drive signal is a sine wave.
In the third aspect of the present invention, the drive signal is a wave except for a sine wave.
In the fourth aspect of the present invention, the synthesizing means synthesizes by joining the plurality of sine waveforms at a center of an amplitude thereof.
The fifth aspect of the present invention is a signal generation circuit for a compound acoustic actuator that generates a sound and a vibration in response to a frequency of a signal input to the compound acoustic actuator, the signal generation circuit comprising: a variable voltage generator to generate a variable voltage, a voltage controlled oscillator controlled by an output of the variable voltage generator and generating a drive signal so as to drive the compound acoustic actuator, a frequency of the drive signal including a resonant frequency causing the compound acoustic actuator to generate the vibration, and a sweeping means to cause the variable voltage generator to generate the variable voltage, repeatedly.
More specifically, the present invention relates to a drive circuit for a compound acoustic actuator, which is mounted in a portable information terminal and which performs notification of a received call by means of vibration, this circuit generating a driving wave that sweeps repeatedly over an arbitrary frequency range, which encompasses the vibration resonant frequency, by using a PCM (pulse code modulation) sound source or the like as the drive circuit.
By adopting the above-noted configuration, it is possible to suppress a reduction in the maximum amount of vibration caused by dispersion in the vibration resonant frequency caused at the time of mounting the compound acoustic actuator. Additionally, by using as the driving waveform a plurality of sine waveforms smoothly joined at the center of the amplitude thereof, with a prescribed frequency interval and period, it is possible to suppress the generation of harmonics, thereby preventing the generation of an abnormal sound.